The invention relates to a method of manufacturing a semiconductor device including the step of depositing from the vapour phase layers on a substrate in the chamber of a reactor in which a vector gas and a reactant gas are introduced.
The term "reactant gas" is to be understood to mean any gas necessary for carrying out an operation or a reaction.
The term "reactor" is to be understood to mean any place or any space in which the operation or the reaction is effected.
The term "vector gas" is to be understood to mean any gas compatible with the reaction or the operation, but not necessarily participating in this operation or reaction. This may be, for example, a completely neutral gas with respect to the reaction or constituting the atmosphere or the medium favourable for a good procedure of the reaction.
The invention is used in the manufacture of active semiconductor devices including epitaxial layers or implanted layers of, for example, materials from the group III-V.
It is known from U.S. Pat. No. 3,930,908 to introduce into the chamber of a reactor for epitaxy from the vapour phase by means of valves of conventional structures gaseous reactant compounds mixed with a vector gas. The regulation, the interruption or the commutation of the flow of these gases then take place, dependent upon the circumstances, by opening or closing cocks or valves causing mechanical elements to be displaced with respect to each other.
However, the use of these conventional cocks or valves proves to be difficult and even impossible in numerous cases and more particularly:
when the gases used are corrosive; PA1 when these gases are polluting and a decontamination is necessary to realize the subsequent commutation with another gas, this decontamination is made difficult due to the fact that the materials constituting the valves are most frequently attacked by the products used for the decontamination; PA1 when these gases have to be kept at a high temperature during their flow, which may be the case with gaseous compounds which are crystallized at the ambient temperature or are solidified: in fact at the high temperature for epitaxy from the vapour phase, such as the temperature lying between 600.degree. and 900.degree. C., the materials satisfying the purity conditions imposed by the epitaxy from the vapour phase are not materials permitting of manufacturing in a simple manner valves satisfying the tightness conditions. Thus, with epitaxy from the vapour phase, metals are excluded because they can contaminate or be attacked by the reactant gas; PA1 when these gases have to be used at very low flow rates or in very small quantities: in fact, the variations of the parasitic pressure due to the commutation can produce errors in the thickness of the epitaxial layers or errors in the doping of the layers formed, which results in that thicknesses of very thin layers, abrupt variations in composition or abrupt variations in doping cannot be obtained by means of the valves of conventional structures. PA1 when these gases have the property that they are adsorbed or desorbed by the materials constituting the tubes transporting them. Thus, the phenomeon of adsorption or desorption of the walls of the tubes after the point of commutation often gives rise to unacceptable memory effects if these tubes are long or cold and especially if these gases to be commuted have molecules having a large bipolar moment. These memory effects can also lead to errors in the thickness of the layers or the doping. PA1 the said second end of the inner tube merges into the intermediate tube, PA1 the said second end of the intermediate tube provided with a restriction merges into the outer tube, PA1 the said second end of the outer tube provided with a restriction merges into the chamber of the reactor in the proximity of the hot zone, PA1 the said first end of the intermediate tube is provided with a valve V, PA1 Since the tube system constituting in itself the valve for introducing the reactant gases into the chamber can be made of a material, such as quartz, which satisfies the purity conditions, epitaxial layers of very high quality can be obatined; moreover, when the tube system is made of such a material, the decontamination, if any, can readily be obtained by means of, for example, a chlorinated gas, which ensures that the method of manufacturing the epitaxial layers is simplified and guarantees that the quality of the layers is maintained in the long run; PA1 the tube system permitting a rapid commutation without any dead space in which the gas remains stagnant and trails of gaseous compounds are produced after commutation, for example, due to the desorption of the walls, thicknesses of very thin layers, abrupt variations in composition or abrupt variations in doping can be obtained; PA1 in general, by means of the method according to the invention, the epitaxial layers or implanted layers are obatined in a simpler manner and are of higher quality.
For all these reasons, the conventional valves have to be avoided.
Therefore, the present invention provides a method of manufacturing, in which these disadvantages are avoided.